In particular, his 18th move, weakening the light squares, was a mistake.

The body is a pattern of dark and light squares.

Another satisfactory definition is that the white king must always be on a light square.

The stout boy flashed his light square on the prisoner.

It also creates a weak light square at d3.

I could see the blocks of six lighter gray squares that were the windows on three sides.

The board is an 8x8 grid, with alternating dark and light squares.

Because the black bishop could not control the light squares, Adams bored in with 32 f5!

Instead, 18 g3 weakened the light squares around his king, a decision that came back to haunt him.

It is safe to be on the very edge of a light red square.